Method of assembling a balanced rotor



B. D. SMITH Nov. 17, 1936.

IETHOD 0F ASSEMBLING A- BALANcEbRoToR Original Filed May 22, 1930 Patented Nov. 17, 1936 WTHQD F ASSEMBLING A IBCEEE'D RWEOR Beecher n. Smith, west Allis, Wis, assignor to Allis-Chalmers Manufacturing Company, Milwaulree, Wis, a corporation of Delaware @riginal application May 22, 1930, Serial No. 54,621. Divided and this application February 3, 1936, Serial No. 62,124

This invention relates generally to an improved method of Constructing a dynamically and also 1 statically balanced rotor which is formed of a plurality of blade segments or the like.

An object of the invention is to provide an improved method of determining the moments of and assembling turbine blade segments or the like, whereby a dynamically and also statically balanced rotor is produced.

This application is a division of application Serial No. 454,621, filed May 22, 1930.

Referring to the drawing: Fig. l is a sectional elevation of the improved scale or apparatus for measuring the moments w of blade segments, or the like, taken on line I-I of Fig. 2 looking in the direction of the arrows. Fig. 2 is a sectional plan of the showing in Fig. 1 taken on line II--II thereof.

Fig. 3 is a side elevation of the scale with a blade segment in moment determining position on the platform thereof.

Fig. 4 shows a pair of blade segments mounted in diametrically opposed relation on -a rotary support 3 5.

In order to obtain a dynamically balanced rotor, consisting of a plurality of blade segments or the like, mounted on a rotary support, a new and novel method of assembling rotors has been devised.

30 the blade segments or the like, prior to assembling and mounting them on a rotary support, are individually measured on an improved scale which will later be described. The moments of the blade segments for a rotary support of a given diameter are all measured under the same conditions. The segment must be generally symmetrically positioned on the platform of the scale with reference to the vertical plane through the 40 platform centerline. The segment is moreover positioned so that the distance from the center of the rotary support engaging surface of the blade segments, or the like, to the pivot or iul- According to this invention the moments of I'he next step in this improved method of balancing rotors is to select two blade segments that have the same value of moments and mount them in diametrically opposed relation on the rotary support as shown in Fig. 4.

Another pair of blade segments having like values of moments is selected and mounted in diametrically opposed relation on the rotary support. Pairs are thus selected and mounted on the rotary support until it has been filled and the rotor completed. I

In order to eiiect a dynamically balanced rotor the centrifugal forces acting on the difierent masses constituting the rotor must have been considered. A body revolving in a curved path of radius R exerts a centrifugal force F, upon the arm or cord which restrains it from moving in a straight line, or flying ofi at a tangent. If W equals the weight of the body, N equals the number of revolutions per minute, g equals the acceleration due to gravity and '0 equals the linear velocity of the center of gravity of the body then substituting the value of p in (1) for o of (2) we get F=0.00034084WRN* From this equation it can be seen that the centrifugal force acting on each of the masses or segments of the rotor is proportional to weight times a certain distance, or a moment. Therefore. by obtaining readings which are proportional to the moments of a plurality of blade segments, or the like, in the manner described above and then mounting the segments in pairs, each segment of a pair having the same moment, in diametrically opposed relation on a rotary support of radius R equal to the distance R at which the moments were determined, the centrifugal forces acting on the pair of segments will be equal and, considering that the pair of segments lie in a space bounded by transverse planes very close together,'these forces will be substantially opposite and the rotor will therefore be practically dynamically and statically balanced. By continuing to fill in the periphery of the support in this manner with the members of each pair having like moments and mounted in diametrically opposed relation on the rotary support a substantially dynamically balanced complete rotor I will be produced.

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The improved scale or moment measuring apparatus already referred to will now be described in detail. The base I carries a standard 2 which forms the support for the beam 3, a knife-edge on the beam engaging the upper portion of the standard. The beam is provided with a major beam scale portion 4 and a minor beam scale portion 5 which carry major and minor traversing poise weights 6 and 1, respectively. A lever I2 is suspended from the beam 3 by means of links In which engage'knife-edges 9 and I on the beam and lever, respectively. The opposite end of the lever I2 is provided with a knife-edge which rests upon the upper portion of a support I3 carried by the base I. A bar 2| positioned perpendicularly to the beam 3 and lever I2 is suspended from lever l2 by means of links l6 and I! linked together and engaging with knife-edges I5 and 22 on the lever and bar, respectively. A knife-edge 19 on the bar 21 near one end thereof and near the knife-edge 22, engages with a standard I8 secured to base Member 20 mounted on base carries at its upper end a trig loop 8. On the free end of the bar 2| a platform 23 is provided which extends to a point near the knifeedge 22 thereof. It will be observed from the drawing that the width of the bar 2| is reduced from a point near the knife-edge 22' to the free end of the bar. This construction permits a slot to be had in the platform, for purposes which will presently appear. Angle irons 25 are secured to the sides of bar 2| so as to have their upper surfaces approximately in the plane of the upper surface of the bar portion that is not reduced in width. Plates 24 are secured to angle irons 25 with their adjacent edges in spaced parallel relation.

' On one of the plates 24 adjacent the slot 26 is inscribed a graduated scale 21 marked in inches as measured from the knife-edge I9. This scale ranges over limits sufficient to cover the minimum and maximum radial dimensions of the rotary supports which are to carry the weighed blade segments. To provide an adjustable means for locating the blade segments on the platform an indicator stop 28 of substantially L shape is provided with a bore to loosely receive a bolt having a square head, of about the size of the thickness of the bar 2 I, at one end, the threaded end of the bolt receiving a wing nut 29 and the head of the bolt is'positioned in the slot 26.

The-operation of the scale is as follows. The stop member 28 is first set at the scale division or reading which corresponds to the radial dimension of the support on which the blade. segments are to be mounted. A blade segment 30 consisting of end shroud and foundation segments 33 and 3|, respectively, and connected blades 32 is then symmetrically positioned on the platform 23 with the mid-portion of the foundation segment 3| in contact with the stop member 28. The major and minor traversing poise weights 6 and 'I are now adjusted on major and minor beam scale portions 4 and 5 respectively, until the free end of the bar 2| stops oscillating and-the beam 3 has its free end positioned in about the center of the trig loop 8. The reading of the two scale portions is then taken in arbitrarily chosen inch units and the value of the moment of this blade segment is represented by this reading.

It should be understood that it is not desired to limit the invention to the exact steps of the process herein shown and described, for .various modifications within the scope of the claims ma occur to persons skilled in the art.

It is claimed and desired to secure by Letters Patent:

1. The method of obtaining a dynamically balanced rotor formed of a plurality of blade segments, or the like, which comprises, individually measuring the moments of a plurality of segments at a distance corresponding to the radius of the rotary support on which they are to be mounted, selecting a pair of segments having the same moments and mounting them in diametrically opposed relation on the support and selecting further pairs of segments, the segments of each pair having like moments, and mounting the'pairs on the support with the segments of each pair in diametrically opposed relation, until the periphcry of the support is filled and the rotor comleted. p 2. The method of obtaining a dynamically balanced rotor formed of a plurality of members of the same conformation and size which comprises, individually measuring the moments of a plurality of members at a distance corresponding to the radius of the rotary support on which they are to be mounted, selecting a pair ofmembers having the same moments and mounting them in diametrically opposed relation on the support and selecting other pairs of members, the members of each pair having like moments, and mounting the pairs on the support, with the members of each pair in diametrically opposed relation until the periphery of the support is filled and the rotor completed.

3. The method of obtaining a dynamically balanced rotor composed of .a plurality of pairs of blade segments, or the like, which comprises individually measuring the moments of a plurality of segments at a distance corresponding to the radius of the rotary support on which they are to be mounted, selecting a pair of segments havin the same moments and mounting them in diametrically opposed relation on the support, and selectinganother pair of segments having like moments and likewise mounting the segments of this pair in diametrically opposed relation in the same transverse plane on the support.

4. Thejmethod of obtaining a dynamically bal-. anced rotor composed of a plurality of pairs of members .or the same conformation which comprises, individually measuring the moments of a plurality of such members at a distance corresponding to the radius of the rotary support on which they are to be mounted, selecting a pair of members having the same moments and mount ing them in diametrically opposed relation on the support, and selecting another pair of members having like moments and likewise mounting the members of this pair in diametrically opposed relation in the same transverse plane on the support.

5. The method of obtaining a dynamically balanced rotor composed of a plurality of pairs of members of the same conformation arranged in a plane perpendicular to the axis of rotation of said rotor which comprises, individually measuring the moments of a plurality of such members at a distance corresponding to the radius of the rotary support on which they are to be mounted, selecting a pair of members having the same moments and mounting them in diametrically opposed relation on the support, and selecting other pairs of members, the members constituting each selected pair having like moments and'mounting the pairs onthe support in said perpendicular plane with the members of each selected pair in diametrically opposed relation, until the periphcry of the support is filled.

6. The method of constructing a dynamically balanced steam turbine rotor from a rotary support having blade receiving positions arranged in a transverse plane and a plurality of steam turbine blade segments, that comprises measuring the static moment of each blade segment about a pivot axis in a plane normal to the radial geometrical axis of said segment and intersecting said axis at a position thereon corresponding to the center of rotation of said segment when mounted in operating position upon a rotor,.se lecting pairs of segments so measured having substantially equal static moments, and filling the blade receiving positions in the transverse plane of said rotary support by mounting the segments of each of said selected pairs in diametrically op posed positions in said transverse plane.

7. The method of constructing a dynamically balanced steam turbine rotor from a rotary support and a plurality of steam turbine segments, that comprises measuring a quantity for each of said segments equivalent to the static gravitational moment of said segment about its axis of rotation when in operating position upon a rotor, and then mounting segments found to have substantially equal static moment values in pairs with the segments of each pair disposed at diametrically opposed positions in the same transverse plane on said rotary support.

8. The method of constructing a dynamically balanced steam turbine rotor having blades arranged in a plane perpendicular to the axis of rotation of said rotor, that comprises measuring the static moment of each of a plurality of turbine blade segments about'a pivot point corresponding to the normal center of rotation of the segment, matching the measured segments in pairs of substantially equal moments, and applying segments of the several pairs to the turbine rotor at diametrically opposed positions insaid plane to thereby fill all of the blade receiving positions in said blade receiving plane of the rotor with opposed matched biade segments whereby a dynamically balanced rotor is obtained.

9. The method of constructing a dynamically balanced steam turbine rotor from a plurality of steam turbine blade segments and a rotary support having blade receiving positions disposed in a transverse plane, that comprises measuring the static moment of each blade segment about a pivot point corresponding in position to the normal center of rotationof the segments, matching the measured segments in pairs in such manner that the segments of each pair have substantially BEECHER D. SIVHTH. I 

